A. Field of Invention
This invention pertains to a process and apparatus for making a wrapping from an endless sheet including the step of pleating the sheet.
B. Description of the Prior Art
As described in French Patent FR 2,595,666-B1 and French Patent of Addition FR 2,628,719, as well as U.S. Pat. No. 4,795,648, a wrapping made of a single thin sheet may be made, for example, for hamburgers as well as other objects having a general convex shape. This wrapping is made, for example, of a single thin sheet of paper which is flexible, or a more complex material or sheet which has a thin piece of paper as a base. The sheet is first formed into a generally elongated rectangular shape which is then pleated with knife pleats extending in parallel to the width of the sheet. Thereafter, the pleats are fixed at their borders in such a manner that the pleats can be opened or deployed only at their central region. There are a large number of methods or means by which the pleats can be fixed including welding or using an adhesive medium. In one preferred version, a sheet of paper coated on one side with a heat weldable material on one surface is disposed on the end of the pleat for fixation. This weldable material is deposited on the paper in a thin layer, for example, by using an aqueous emulsion to deposit a film of plastic on the paper. The pleated sheet produced in this manner is advantageous in that it is easy to cut and resists peeling.